The present invention relates to manufacturing fiber optic cable, and more particularly relates to an apparatus for the application of a binder about a bundle of optical fibers.
An increased volume of Internet use and the desire to send and receive data-intensive multimedia applications have greatly increased the demands put on the existing communications infrastructure. This has led to a push for greater bandwidth capabilities through the use of fiber optic cables in lieu of traditional copper cables. Increased demand for fiber optic cable has resulted in a need for ever-increasing production rates for cable winding machines.
Fiber optic cable of various configurations are in use for communications. In many commonly used types of cables, the optical fibers are encased in protective buffer tubes which are formed of a flexible plastic material. Such fiber optic cables also often include a central reinforcing member about which the buffer tubes are arranged to provide strength to the cable. After the buffer tubes have been positioned around the central reinforcing member, yarn-like binders are wound around the buffer tubes to retain the buffer tubes in position against one another and the central reinforcing member. A plastic sheath or jacket is then provided over the binder and buffer tubes for added protection.
Various winding techniques for helically winding buffer tubes around the central reinforcing member have been employed. One advantageous method is to arrange the buffer tubes around the central reinforcing member using a reverse oscillating lay technique. The buffer tubes are provided from non-orbiting supply sources and advanced in a direction generally parallel to the central reinforcing member. One or more lay plates are provided having a central opening for the central reinforcing member and a plurality of radially spaced openings about the central reinforcing member. From the most downstream lay plate, the buffer tubes converge towards the central reinforcing member at a closing point and are laid against the central reinforcing member in an oscillating lay. Typically, eight turns are applied in one direction before reversing to the opposite direction. This technique is also known as xe2x80x9cS-Zxe2x80x9d stranding in reference to the appearance of the oscillated buffer tubes once engaged against the central reinforcing member.
The buffer tubes and central reinforcing member are then advanced through an aluminum or steel binder head of a binder device where the binder is wound around the buffer tubes. The binder device may also include a second binder head positioned downstream of the first binder head for winding a second binder around the buffer tubes in an opposite direction. A binder head of this type is illustrated in U.S. Pat. No. 4,325,212 to Hope nee Swiecicki. As illustrated in FIG. 2, the binder head includes a binder reel rotatably supported on a hollow shaft which surrounds the fiber optic cable. The shaft is supported at its downstream end on bearings and has an upstream free end. The shaft and the binder reel are rotated by a conventional belt-and-pulley drive. As the reel is rotated, one or more binder guides pay out the binder over the free end of the shaft so that it can be wound around the buffer tubes. A capstan is typically provided downstream of the binder heads for pulling the fiber optic cable through the apparatus.
Current cable winding machines are limited in their production rates because the binder has to run at high speeds to get a meaningful cable production rate. In addition, the tension in the binder as it is applied must fall within stringent tolerances on the order of xc2x110%. Typically, binders are applied on the cable at a pitch, or lay length, of between 15 mm and mm, most commonly 20 mm. Actual running speeds of binder application machines is currently limited to 3600 to 3800 RPM, which translates into a cable line production speed of about 76 meters per minute at a 20 mm pitch. An increase of the rotational speed of the binder applicator to even 5000 RPM would result in a 32% cable line production speed increase at the same 20 mm lay length.
It is generally difficult to achieve rotational speeds that exceed 4000 RPM with many existing binder devices because of a concomitant increase in centrifugal forces and vibration loads on the binder device. Such high centrifugal forces may break or damage the binder device. Aluminum binder heads typically weigh over 8 kg each and may structurally fail due to centrifugal forces at a rotational speed of 4000 RPM which results in a loss in cable production time.
Beyond binder head failure, the useful life of the binder device can be reduced by the existence of centrifugal forces, vibrations and other loads. Vibration can result from various sources including unbalance of one or more of the drive components for the binder head, or of the binder head itself. For instance, an unbalance of one gram located at a 100 mm radius and rotating at 5000 RPM results in a centrifugal force of 6.24 lbs. In some existing binder devices, the vibrations of the drive components have harmonics at around 3200 to 3400 RPM that coincide with the harmonics of the tubular shaft, which can cause a forced resonance of the shaft that may lead to failure of the shaft. In addition, the vibration loads and the weight of the binder head cantilevered from the end of the shaft degrade the bearings supporting the shaft. Tension in the pulley of the belt-and pulley drive system adds to the detrimental loads on the shaft and bearings.
Therefore, it would be desirable to increase fiber optic cable production speeds by increasing the speed of binder application without decreasing the useful life of the binder applicator or the creation of a situation where there is a structural failure of the binder head.
The present invention addresses the above needs and achieves other advantages by providing a high-speed binder device for binding together various components of a cable, especially a fiber optic cable, in which a binder head or a guide drum for guiding a binder is formed of a lightweight synthetic material, such as a carbon fiber composite material, that reduces the occurrence of increased loads and vibrations at speeds above 4000 RPM. The lightweight material preferably has a substantially higher strength-to-weight ratio than more conventional materials, such as aluminum or steel. The increased rotational speeds allowed by the present invention can result in a double-digit percentage increase in cable line production speeds. Increased production speeds are desirable considering the increasing demand for fiber optic cable.
The high-speed binder device comprises a frame supporting a binder reel. A supply of binder is wound on the binder reel and the binder reel rotates on the frame. The binder reel defines a central opening through which the cable to be bound is advanced. A guide drum is also rotatably supported on the frame and is operatively connected to the drive motor for paying out binder from the binder reel and wrapping the binder around the cable. Constructing the guide drum of a lightweight synthetic material allows the guide drum to be rotated at a high rate of speed without failing or excess loading of the binder device and its bearings.
Preferably, the guide drum is comprised of a composite material, such as a carbon fiber material, although other lightweight synthetic materials such as high-strength plastics could be used. The guide drum defines a tubular shape that has a substantially cylindrical wall with a radial thickness of approximately xe2x85x9of an inch. The tubular shape has an open end and a closed end. The closed end comprises an aluminum hub to which the fiber composite wall is adhered with an epoxy material. In this configuration, the guide drum comprised of carbon fiber weighs less than 4 lbs., and more preferably weighs approximately 3.6 lbs., as compared with about 18 lbs. for a conventional aluminum drum.
The low weight and high strength of the carbon fiber material allows the guide drum to withstand higher rotational speeds in excess of 4000 RPM. The decreased weight of the cantilevered guide drum decreases the loads exerted on the shaft, bearings and other components of the binder device. The decreased weight of the guide drum also reduces unbalanced loads and allows for operation with relatively low vibrations at higher rotational speeds.